In photography, exposure relates to an amount of light per unit area reaching a photographic film or image sensor. A camera in an automatic exposure (AE) mode automatically calculates and adjusts exposure settings.
High Dynamic Range (HDR) photo techniques are used to capture images in which the scene content has very bright and very low level light regions, sometimes called a high dynamic range scene. A high dynamic range scene presents problems for standard imaging systems because the exposure value (combination of exposure time and gain) is fixed for the entire frame.